The present invention relates to a method for fabricating metal interconnections used for flat panel displays such as liquid crystal displays (LCD), plasma display panels (PDP), electrochromic displays (ECD) and electroluminescent displays (ELD), or flat panel sensors such as X-ray imaging devices.
In a flat panel display typified by LCD, normally, display material such as liquid crystals or discharge gas is sandwiched between a pair of insulating substrates, and electrical interconnection lines are arrayed on at least one of the insulating substrates, where a voltage is applied to the display material via the electrical lines.
For example, in the case of an active matrix drive type LCD, a plurality of gate electrodes and a plurality of data electrodes are provided in a matrix shape on an active matrix substrate, which is one of the pair of insulating substrates between which the display material is sandwiched. At intersections of these gate electrodes and data electrodes, thin film transistors (TFT) and pixel electrodes are provided every intersection. Normally, these gate electrodes and data electrodes are made of metal material such as tantalum (Ta), aluminum (Al) or molybdenum (Mo), and deposited by dry deposition process such as sputtering process.
In such flat panel displays, in an attempt to implement larger areas and higher definitions, increased drive frequencies would cause the resistance of the electrical lines as well as the parasitic capacitance to increase. As a result of this, delay of driving signals would come up as a large problem.
Thus, in order to solve the problem of the delay of driving signals, there has been made an attempt to use Cu (copper, bulk resistivity: 1.7 μΩ·cm) having lower electrical resistance as the interconnection material, instead of Al (bulk resistivity: 2.7 μΩ·cm), α-Ta (bulk resistivity: 13.1 μΩ·cm) or Mo (bulk resistivity: 5.8 μΩ·cm), which are conventional interconnection materials. For example, “Low Resistance Copper Address Line for TFT-LCD” (Japan Display '89, pp. 498-501) discloses discussion results on a case of using Cu as the gate electrode material of TFT-LCD (thin film transistor liquid crystal display). According to this literature, it is pointed out that because a Cu film deposited by sputtering process is poor in adhesion to the ground glass substrate, a ground metal film of Ta or the like needs to be interveniently provided between the ground glass substrate and the Cu film in order to enhance the adhesion to the ground glass substrate.
However, in the case of the interconnection structure shown in the above literature, separate deposition processes are involved for the Cu film and the ground metal film of Ta or the like, causing a process increase and leading to a cost increase, as a disadvantage.
Also, separate etching processes are involved for the Cu film and the ground metal film of Ta or the like, causing a process increase and leading to a cost increase, as a disadvantage.